1. Field of the Invention
The present invention relates to actuators that are made to actuate by using ultrasonic vibration and methods for driving the same.
2. Description of the Related Art
Oscillatory-wave actuators such as ultrasonic motors (USMs) form a plurality of standing waves whose positions are shifted according to their time of generation in elastic bodies, and drive movable bodies that are in contact with the elastic bodies according to traveling waves formed by synthesizing the plurality of standing waves. In general, such oscillatory-wave actuators are driven by applying two or more alternating (AC) voltages whose phases are shifted relative to each other. Japanese Patent Publication No. 05-88074 discloses a technology of applying a single-phase voltage to another voltage that has been phase shifted by phase retardation by use of an inductor when an oscillatory-wave actuator is driven by a single-phase high-frequency AC-power circuit.
Also, Japanese Patent Laid-Open No. 05-284764 discloses a technology for enabling a reduction in the size of an oscillatory-wave actuator by applying AC voltages boosted by a piezoelectric transformer. However, the technology disclosed in Japanese Patent Publication No. 05-88074 requires inductor elements in addition to an oscillator.
Moreover, mechanical resonance and electrical resonance need to be matched with each other. Moreover, the technology disclosed in Japanese Patent Laid-Open No. 05-284764 requires an oscillator for the piezoelectric transformer in addition to the oscillator for the USM. Also, the resonance frequency of the piezoelectric transformer and that of the oscillatory-wave actuator need to be matched.
It would be desirable to provide an oscillatory-wave actuator having a simplified design which would require less components. For instance, it would be desirable to provide an oscillatory-wave actuator that forms a traveling wave in the elastic body by use of a single-phase driving voltage without requiring a driving circuit generating multi-phase AC voltages.